This is how you get from Tauren territory (Thunder Bluff, Mulgore) to Orc and Troll territory (Orgrimmar, Durotar).
As of patch 3.2.0 you can take a zeppelin between the two cities. Thunder Bluff's departs from the northwestern dock onSpirit Rise; Orgrimmar's departs from the western dock of the western zeppelin tower atop the Orgrimmar Skyway. Waiting for the zeppelin can take up to 10 minutes, though, so it requires a bit of patience to use.
There is a road south from Thunder Bluff that T's at Bloodhoof Village.
Go east at the T and continue east as you see a pass through the mountains to the west-most edge of theSouthern Barrens and Ruins of Taurajo.
Follow the road through the ruins east until you hit a T just east of them and go north. Watch out, because the Barrens creatures can be quite dangerous to low level characters.
Continue north passing into the Northern Barrens and to the Crossroads (where there is a Flight Master). In Crossroads you will pass a road branching east to Ratchet (where there is a Flight Path too as of 1.11), if you want to take a boat to Booty Bay.
At the Crossroads take the road north until it is intersected by a road from the east.
Take the eastern road and continue east, past Far Watch Post and over the bridge across the Southfury River, until you get to Razor Hill.
Razor Hill is where the road from the Northern Barrens hits the main north-south road.
Take the road north to Orgrimmar or south to Sen'Jin Village.
Also, if you have the flight path from Thunder Bluff to Orgrimmar, you can just fly there for an affordable 50 copper.